1. Field of the Invention
The present invention relates generally to sheet processing apparatuses and image forming systems and, more particularly, to a sheet processing apparatus that performs predetermined processing, such as aligning and stapling, on a sheet member (e.g., sheet-like recording media in general, including recording sheets, transfer paper, and an OHP sheet) conveyed therein, and an image forming system including the sheet processing apparatus and an image forming apparatus.
2. Description of the Related Art
Known techniques of this sort are disclosed in Japanese Patent Application Laid-open No. 2007-153552, Japanese Patent Application Laid-open No. 2007-153605, and Japanese Patent Application Laid-open No. H11-180628. Of these, Japanese Patent Application Laid-open No. 2007-153552 discloses a sheet processing apparatus that includes, with the aim of offering a simple structure having one drive source and a wider range of choice of stapling positions, a stapling unit that staples sheet members conveyed therein, a unit that moves the stapling unit in a direction orthogonal to a sheet member conveying direction, and a single drive source that drives the unit for moving the stapling unit. The sheet processing apparatus disclosed in Japanese Patent Application Laid-open No. 2007-153552 further includes another unit that, during the process in which the moving unit moves the stapling unit, causes part of the stapling unit to abut against a protrusion formed at a predetermined position to thereby rotate the stapling unit.
Japanese Patent Application Laid-open No. 2007-153605 discloses a sheet processing apparatus that aims at achieving reduction in the size of the apparatus and space-saving, and guaranteeing high stapling quality. The sheet processing apparatus includes a first support member that abuts against an end portion of the sheet member upstream in a sheet member conveying direction during aligning of a sheet member, a second support member that supports other portions of the sheet member, and a sheet stapling unit that staples the sheet member. In the sheet processing apparatus disclosed in Japanese Patent Application Laid-open No. 2007-153605, the sheet stapling unit has a stapling direction that extends in parallel with a surface of the first support member in abutment with the end portion of the sheet member. The sheet processing apparatus further includes a rotating unit that moves the sheet stapling unit in a direction orthogonal to the sheet member conveying direction using a single drive source to thereby rotate the sheet stapling unit through a predetermined range. During the process in which the rotating unit moves the sheet stapling unit, the sheet stapling unit is rotated with part thereof made to abut against a protrusion formed at a predetermined position.
Japanese Patent Application Laid-open No. H11-180628 discloses a sheet post-processing apparatus that, with the aim of facilitating and expediting assembly adjustment and service procedures by simply constructing stapling process components of the sheet post-processing apparatus, performs a stapling process for sheets on which images have been formed conveyed from an image forming apparatus before discharging the sheets into a discharge tray using a discharging unit. The sheet post-processing apparatus disclosed in Japanese Patent Application Laid-open No. H11-180628 further includes a pair of staplers that perform a stapling process for the sheets of various sizes on which images have been formed, the staplers being configured to be driven for translation and rotation by a single drive source. For sheets of various small sizes, the staplers are translated for a stapling process in a width direction orthogonal to a sheet conveying direction and, for sheets of various large sizes, the staplers are translated and rotated for a stapling process. In addition, each of the staplers is rotated by a cam plate fixed to a sheet post-processing apparatus main unit and a cam follower fixedly mounted on the stapler.
The technique disclosed in Japanese Patent Application Laid-open No. 2007-153552 holds a stapler at an angular position for oblique stapling through hooking onto a claw. Hooking a heavy stapler onto the claw as described above poses a problem in that repeated hooking and unhooking operations cause sag, or in the worst case, break the claw. The technique also poses a problem in that the claw is unable to hold the weight of the stapler, if an aligning (stapler tray) angle is acute.
The technique disclosed in Japanese Patent Application Laid-open No. 2007-153605 holds a stapler at an angular position for oblique stapling with a spring. To hold the stapler at an angular position only with a spring, the spring needs to offer a high load capacity to sustain the weight of the stapler. This increases motor load required for changing posture through abutment, resulting in a problem of an additional need to increase motor current. If the aligning angle is acute, the spring load needs to be further increased, which increases motor load with a resultant further increase in current.
The technique disclosed in Japanese Patent Application Laid-open No. H11-180628 holds the stapler at an angular position for oblique stapling with a guide rail. The guide rail limits a range over which oblique stapling can be performed, defying stapling at a central position. This poses a problem of not being able to respond to users' needs.
There is therefore a need to enable reliable oblique stapling without involving increased motor current, enable stapling at a wide range from the center to end portions and enable oblique stapling of various sheet sizes.